Wearers of hearing aids have a large problem in that transient interfering sounds which are of only short duration such as, for example, clattering of dishes, crackling paper and the like, are amplified to a comparatively high level. These transient interfering sounds are in most cases felt to be excessively loud and very disturbing, therefore.
At present, no hearing aids are available on the market which have an algorithm which especially counters such transient interfering sounds. The reasons for this are that in the application of hearing aids, the transient interfering sound must be attenuated extremely quickly and strongly. In addition, the attenuation must be implemented in real time, i.e. without the output signal being noticeably delayed. As a rule, however, this is associated with audible artifacts since the speed of regulation falls into the range below single periods of the time signal of, e.g., the voice.
Transient interfering sounds are attenuated only inadequately by hearing aids with AGC (Automatic Gain Control). With AGC, rapid input-level-dependent control is implemented but the higher the level, the more this control intervenes in the signal. However, this is not practicable for a short signal such as transient interfering sounds.
From the printed document DE 37 33 983 A1, a method for attenuating interfering noise in sound signals transmitted by hearing aids is known. In this arrangement, spectral distributions of the signals are obtained by a Fourier analysis. The respective spectral distribution is divided into different frequency windows via filters. Following that, the change in the spectral distribution with time in the respective frequency window is determined. Thus, the envelope curve of the spectral distributions is monitored over time for the individual frequency windows. Depending on control signals in the individual frequency windows, the amplitudes of the interfering signals are lowered in the respective spectral distribution. The spectral distribution thus “cleaned up” is transformed back into the time domain.
In addition, a method for detecting and generating transient conditions in sound signals is described in printed document DE 694 17 445 T2. To extract information from the form of the energy changes, the forms of the energy changes are represented by the form of a transient pulse of the signal. An envelope curve detection is preferably used. Furthermore, slope and/or change in slope of a part of the front edge is registered.
Printed document DE 600 10 273 T2 also discloses a multi-channel cochlear implant with neural response telemetry. In this arrangement, the envelope curve of an input signal is detected in the cochlear implant.
Furthermore, a method and a device for the reduction of interfering noise are known from printed document WO 01/52242 A1. In this device, the ratio of a signal envelope curve to a noise envelope curve is used for adjusting an amplifier function.
The U.S. Pat. No. 3,458,669 discloses devices for studying or treating acustic phenomena. Such devices or hearing aids serve to replace defective portions of an ear. The devices are arranged in such manner as to detect the importance of the sound impulses contained in these phenomena, in particular in order to determine—and possibly to reduce—the degree of noxiousness of said impulses for the ears of the hearers or again to set up electric terms representative of the acoustic sensations truly perceived by the hearers of said phenomena. For this purpose, the device includes a system for differentiating signals, means for collecting other portions of the signals before their differentiation and for sending said other portions to an earphone capable of transforming it into sounds and means capable of preventing the transfer of the other portion of said earphone at the times when the amplitude of the corresponding differentiated signals exceeds a predetermined threshold.
The further document EP 0 290 415 A1 discloses a sound surge detector for a alerting headphone users. For appliancies or devices transmitting data originating from a sound source and directed at headphones, the warning method provides for a pick-up of external ambient signals followed by their processing in order to generate a control signal when an emergence of given minimum characteristics is detected. The signal provides for activation of a warning signal and its transmission to the headphones.
A method for damping transient sounds, preferably in hearing aids is described in document WO 83/02862 whereby the derivative of the incoming sound signal is calculated. The transient eliminator is adapted to discriminate transient sounds in a complex sound signal and thereafter to selectively eliminate the same. The method is attained in that the main derivative of the sound signal controls the damping of uncomfortable transients occurring in the audio signal. It is thus the object of the present invention to propose a method which allows transient interfering sounds to be perceived as less disturbing. In addition, a corresponding hearing device is to be specified.